Vitreous glass sealed beam lamp units have been used for vehicle lighting since at least the 1930's in the United States. These lamps generally include a paraboloidal reflector having a highly mirrorized inner surface that usually has two central openings that receive connectors for a filament aligned within the reflector. The reflector is enclosed by a circular convex lens also constructed of glass that is located with respect to the reflector by various types of integral locating tabs and is joined to the reflector by heat fusion. The connector assemblies are also usually connected to the reflector by a heat fusion process, and the composition and pressure of gas within the reflector-lens envelope are carefully controlled through a filling tube formed integrally with the reflector, and this tube is fused after evacuation and/or, inert gas filling of the lamp envelope. Controlling the atmosphere within the evenlope through the filling tube is extremely costly, and the filling tube must be carefully fused at the proper instant to achieve the desired atmosphere within the envelope.
Such a sealed beam lamp unit is shown and described in the D. K. Right U.S Pat. No. 2,148,314 dated Feb. 21, 1939.
These sealed beam lamp units, which must be replaced after the filaments burn out, require complicated locking rings and adjustment assemblies, permanently carried by the associated vehicle to hold them in proper position. The locking rings frequently include adjusting brackets for varying the attitude of the lamp units to properly adjust the lamp's beam to effect the desired lamp alignment.
It has been suggested that the reflector of a rectangular sealed beam lamp unit be constructed of a plastic material with support flanges formed integrally with the plastic to eliminate the complicated mounting flanges and rings required in prior lamp units. Such a construction is shown in the Thomas T. Talon et al U.S. Pat. No. 4,188,655. This patent discloses a lamp with three integral flanges on a plastic reflector that cooperate with three adjusting assemblies mounted to the vehicle that permit adjustment of the lamp beam in two orthogonal planes. While such an arrangement is suitable for many passenger automobile applications it is nevertheless quite costly because of the three separate fastening and adjusting mechanisms required.
The prior manufacture of lamp units has also included the provision of a vent hole in the reflector to permit the escape of gases evolving during the heating steps. One method for sealing this vent hole that has achieved some limited success, is to place a common headed rivet in the vent hole and then backfill the hole with an adhesive material. The rivet serves merely to prevent entry into the lamp envelope by the adhesive material. While this method provides an acceptable seal, the additional cost of the rivet and the labor required for its insertion contribute significantly to the cost of the completed lamp unit.